Method of studying earth formations employing acetylene as a tracer gas



Patented Mar. 18, 1952 METHOD OF STUDYING EARTH FORMA- TIONS EMPLOYING ACETYLENE AS A TRACER GAS Donald 0. Bond, Northbrook, and Michael Savoy,

Chicago, Ill., assignors to The Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. ApplicationApril 24, 1947, Serial No. 743,728

Claims. .(Cl. 23232) This invention relates to methods for secondary recovery ofoil from earth formations and particularly, it relates to a method for the determination of earth porosity in the aid of secondary recovery.

It is common practice in oil fields to employ water to promote flow of oil to wells becoming exhausted.- This is carried out by pumping water under pressure into a dry well to force oil into adjacent formations for recovery from adjacent wells. Another process employs air or gas to induce flow to unproductive wells. Essentially, the methods are alike for they employ fluids to force the flow of oil into desired strata.

In any secondary recovery method adopted, it is essential that the operator know something about the earth formation in order to employ the recovery fluid to the greatest advantage. For example, knowledge of the direction, rate or extent of flow of injected fluids into an earth formation greatly facilitates the choice of secondary recovery technique employed. Accordingly;

it is a fundamental object of our invention to provide a simple method of studying earth formations in order to permit operators to determine the nature of secondary recovery methods which should be adopted.

It is a second'object of the invention to provide a method of studying earth formations which is simple enough for field use and within the skill of the ordinary oil fleldhand.

It is a third object of the'invention to provide a method. of following the course of injection fluid whether it be gas or liquid.

Other objects and advantages of the invention will in part be obvious and in part appear hereinafter.

Our invention, accordingly, relates to an improved method for studying earth formations and for recovering oil retained in these formations by forcing'it from the wells, which method involves injecting a fluid, such as a natural gas or water, or other fluid which is not reactive with acetylene under the conditions of use, into the earth formation, including with thefluid about 1 per cent of acetylene, and determining the points to which the acetylene penetrates, If the fluid used isa gas,- aboutl per cent of-acetylene is adequate; if the fluid is water, it should be substantially saturated with acetylene. Since acetylene does not occur in natural gas or with petroleum, its appearance at any point removed from the point of injection is an indication of direct connection between that point and the point of injection. We have found that acetylene will flow great distances through earth formations and be retained in the carrierfluid in detectable amount.

Gas mixtures which are useful for purposes of this invention may contain as little as 1 part of acetylene in 100,000, because methods for the detection of acetylene are sensitive to levels well below that indicated. Also, in passing through the earth formations, acetylene does not undergo any reactions which result in its being consumed and failing to appear at test points. Where the crude being pumped from the well is sour and shows appreciable quantities of hydrogen sulfide, interference of hydrogen sulfide with the test for acetylene can be avoided by passing the gas through an alkali absorbent before testing for acetylene.

For low pressure injection, encountered where wells have been pumped under vacuum, the acetylene can be employed undiluted and passed directly into the injection gas. -In situations where it is necessary to employ the injection gas and hence the acetylene under substantial pres sure, the acetylene should be diluted with 25 to 50 per cent or more of nitrogen or other inert gas, such as carbon dioxide, to avoid danger of explosion.

Where the injection fluid to be used is water or brine, it is advisable to employ a substantially saturated solution of acetylene. Since acetylene at about ambient temperature and pressure is soluble in water to the extent of about 1 volume of gas per volume of water and is detectable in much smaller concentrations, the course of'th'e water through earth formations can be easily followed.

The method of carrying out a study of an earth formation preparatory for secondary recovery in accordance with this invention is given in the following example describing a test conducted in an Oklahoma oil field.

Example I.Gas consisting of'natural gas and acetylene was injected into a well at a rate of about 25,000 cubic feet per day. One per cent of acetylene was mixed with the injected gas; In

order to avoid the possibility of explosion induced by compressed acetylene, the injection was car ried out at low pressure of the order of about pounds per square inch. This was quite possible because the producing wells in the area had been operating under vacuum. Injection of the acetylene was continued for three days during which period about 750 cubic feet of acetylene was used. The acetylene was detected in producing wells about 400 feet away from the injected well within 48 to 96 hours after starting the injection. In several of the cases, the acetylene continued to flow in the well where it was found in detectable concentration some 24 to 48 hours after its initial appearance.

The sampling of the gas from the producing wells and the testing thereof for acetylene was carried out by bubbling a sample of the gas through Ilosvay reagent (W. Riese, Zeit, f. angewz, Chem., 44, 701-3, 1931). When acetylene in low concentrations is contacted with the test solution, it forms a red precipitate which may appear in various shades depending upon the amount of acetylene, because of the formation of colloidal red cuprous acetylide. These solutions are prepared as follows:

Solution A.-Two, grams of chemically pure copper nitrate was dissolved in milliliters of distilled water in a 100 milliliter volumetric flask. Eightgrams of solid hydroxylamine hydrochloride was added and the solution shaken until the Solid'dissolved. The mixture was then decomposed by the addition of 10.5 milliliters of aqueous ammonia containing 20 grams of ammonia per 100 milliliters. Six milliliters of freshly prepared 2 percent gelatin solution was then added, the mixture was stirred, and then diluted to 100 milliliters with distilled water.

Solution B.-This was prepared by mixing the follovm'ng solutions: (1) Solution containing 20 grams copper sulfate, 80 milliliters concentrated ammoniumihydroxide. and 500 milliliters water; (2) 90 grams hydroxylamine hydrochloride in 500 milliliters Water; ('3) 1 gram gelatin in 200 milliliters water. Solution B was prepared by mixing 2 volumes of (1), 2 volumes of (2), and 1 volume of (3).

It. is known that by measuring the amount of acetylene and injection fluid forced into an earth formation per unit of time and the time of first appearance of the tracer in neighboring formations orthe. amount of acetylene and injection fiuldappearin'g therein, information can be obtained as to the flow characteristics of the earth formation being treated. Since the acetylene is detectable in very small concentrations at these remote points, the presence of oil or water or both in the formation is no deterrent to the accuracy of the results. It was found experimentally that there is no serious. danger of losing a large portion of the injected acetylene by solution thereofin gas, water or oil in the well, for the-solubility of acetylene in the oil and water is such that when used at, a. concentration of about 1 'per cent in the injected gas, there is an ample quantity left to flow through the earth formation and be detected at test points.

Likewise, we have experimentally shown that acetylene is detectable in quantities as small as one part in 600,000 in natural gases consisting largely of methane. It is detectable also in aqueous and brine solutions in amounts as small as one part in 2500-. The table summarizes a few test results indicating the detectability of acetylene in fluid carriers:

Acetylene Concentration given as a ratiovolume of acetylene per volumes of carrier.

Gas samples listed were each 1 liter.

3 Water samples were 5 milliliters.

4 A typical oil well brine; brine samples were 5 milliliters.

The high solubility of acetylene in water and the ease with which it can be detected makes it possible to use it as a tracer in water injection operations for extremely dilute solutions of the gas can be used. Therefore, when water is used as a carrier the volume ratio of acetylene to water may be of the order of 1 to 5,000. It is not lost in its course through the earth, and it can be detected in minute concentrations. Solutions of acetylene containing as little as one volume of the gas in 400 volumes of water will give a light pink coloration with the test described. Similarly, brines, which commonly occur in oil strata. will dissolve acetylene, to a lesser extent than pure water, but will give positive indication of the presence of the gas in solutions containing one volume'of the acetylene in 2500 volumes of brine,

Information as to the time of appearance of the first detectable amount of acetylene tracer in the injected fluid arriving at remote points from the injection well is useful in estimatin the rate and direction of migration of fluids in the formation and serves to'confirm or augment results of previous permeability determinations made on core samples therefrom, electric log correlations, drilling records and. bottom hole pressure studies etc. relating to the establishment of the probable existence and location of crevices and fissures, faults or impermeable barriers with- 'in the formation studied. This information is a valuable guide in adopting the most economical and productive secondary recovery technique.

It is apparent to those skilled in the art that the above matter is merely illustrative and should not be construed as limiting the invention in any way, and that changes may be made in the process without departing from the spirit and scope of the invention.

What is claimed is:

1. The method of studying earth formations in the neighborhood of an oil producing formation to determine their flow characteristics as an aid to the secondary recovery of oil therefrom comprising, injecting into the formation a fluid not reactive with acetylene under the conditions of operation, the fluid containing a small amount of acetylene, withdrawing a sample of said fluid from the earth formation at a point removed from the point of injection, and testing the fluid for the presence of acetylene.

2. The methodin accordance'with claiml in which the injected'iluid is a gas containing about 0.001 to 1 volume of'acetylene per volumes of gas.

3. The method inaccordance with claim l-in which the injected fluid is a natural gas containing about 0.001 to 1 volume of acetylene per 100 volumes of gas.

4. The method in accordance with claim 1 in which the injected fluid is Water containing about 1 volume of acetylene in 1 to 5000 volumes of water.

5. The method of studying earth formations adjacent a well bore to determine the flow characteristics as an aid to the secondary recovery of oil therefrom comprising injecting into said well bore water substantially saturated with acetylene thereby to enter said formations, withdrawing samples of water from said formations at points removed from said well bore and testing said samples for the presence of acetylene.

DONALD C. BOND. MICHAEL SAVOY.

6 REFERENCES CITED The followingieferences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,348,985 Lewis May 16, 1944 2,414,913 Williams Jan. 28, 1947 2,429,577 French Oct. 21, 1947 FOREIGN PATENTS Number Country Date 573,759 Germany Apr. 5, 1933 825,443 France Nov. 12, 1938 OTHER REFERENCES Reise Zeitschrift fur Angewandte Chemie," vol. 44, pages 701-703 (1931). 

1. THE METHOD OF STUDYING EARTH FORMATIONS IN THE NEIGHBORHOOD OF AN OIL PRODUCING FORMATION TO DETERMINE THEIR FLOW CHARACTERISTICS AS AN AID TO THE SECONDARY RECOVERY OF OIL THEREFROM COMPRISING, INJECTING INTO THE FORMATION A FLUID NOT REACTIVE WITH ACETYLENE UNDER THE CONDITIONS OF OPERATION, THE FLUID CONTAINING A SMALL AMOUNT OF ACETYLENE, WITHDRAWING A SAMPLE OF SAID FLUID FROM THE EARTH FORMATION AT A POINT REMOVED FROM THE POINT OF INJECTION, AND TESTING THE FLUID FOR THE PRESENCE OF ACETYLENE. 